1. Field of the Invention
The present invention relates to a thermoelectric-cooling temperature control apparatus located in a clean room for maintaining a constant temperature inside a semiconductor device fabrication facility.
2. Description of the Related Art
In general, semiconductor devices are fabricated by executing various processes repeatedly. The conditions in the semiconductor device fabrication facility must be well regulated in order for the fabrication processes to be carried out precisely and efficiently. These conditions include temperature, vacuum pressure, radio frequency power, gas flow rate, etc. However, if any one of the above conditions is not kept stable during the respective process carried out thereunder, productivity is adversely affected, e.g., the production yield, etch rate, uniformity, etc., is reduced.
Recently, wafers having a large diameter(greater than 300 mm) have been used for mass producing highly integrated semiconductor devices. Accordingly, each piece of processing equipment has been adapted for use with such wafers. Also, accessory equipment is required for regulating the process conditions appropriately for the processing of the large wafers.
In particular, the semiconductor device fabrication processes include a dry etch process in which a wafer is etched by activating process gas inside a process chamber, whereby the process gas assumes the state of plasma. In the dry etch process, a certain portion of a layer grown on the wafer is selectively etched by the process gas in a plasma state, using a photoresist as a mask. Dry etching is an important step for fabricating high-capacity and highly integrated semiconductor devices. The types of plasma which are used are referred to as Capacitive Coupled Plasma (CCP) and Inductive Coupled Plasma (ICP).
Capacitive Coupled Plasma is produced by an electric field generated by selectively applying high frequency power to a plurality of electrodes installed inside the process chamber. On the other hand, Inductive Coupled Plasma is produced by magnetic and electric fields respectively generated by selectively applying high frequency power to coils wound around the outside of the process chamber and to a plurality of electrodes installed inside the process chamber. In addition to the dry etch process, plasma is also typically used in a Chemical Vapor Deposition (CVD) process to form a good thin layer on a wafer inside a process chamber.
In the above-described processes for manufacturing semiconductor devices, at least two electrodes are required to form the plasma, and a wafer is mounted on either one of the two electrodes. Most important, though, the process conditions, i.e., process temperature, must be regulated appropriately if the process is to impart the desired characteristics to the semiconductor device. Therefore, a chiller as a heat exchanger is provided outside the semiconductor device fabrication facility for automatically controlling the temperature within the chamber.
The chiller is of critical importance in the dry etch process. The chiller prevents the electrodes (cathode or anode) from overheating during the etch process and maintains the temperature inside the chamber to within a certain temperature range, thereby preventing the dry etch apparatus from malfunctioning due to temperature fluctuations.
FIG. 6 schematically illustrates a chiller (heat exchanger) of a semiconductor device fabrication facility in which plasma is produced.
The semiconductor device fabrication facility (F) includes an electrode 132 provided at the bottom of a chamber 130, a pedestal 134 on top of the electrode 132, and a second electrode 131. The pedestal 134 is provided with the same electric potential as the electrode 132. An electric state chuck (not shown) is incorporated into the pedestal 134 and supports a wafer 2 thereon. The electrode 131 surrounds the electrode 132 and the pedestal 134 to form a sealed space therebetween. An insulator 133 is disposed around the electrode 132 and the pedestal 134 to provide electrical insulation between the electrode 131 and the electrode 132.
In addition, a vacuum port 135 is provided on one side of the electrode 131. The vacuum port 135 is selectively opened to maintain a vacuum in the sealed space. A vacuum pump (not shown) is connected to the vacuum port 135 to create the vacuum in the chamber 130. A gas supply line (not shown) is open at one side of the chamber 130 to fill the sealed space with process gas. A high frequency power source (RF) is connected to the bottom of the electrode 132, and the electrode 131 is connected to ground.
As the vacuum pump is operated to produce a high vacuum state in the chamber 130, process gas fills the sealed space of the chamber 130. The wafer 2 is processed by the process gas when high frequency power is applied to the electrode 132, and the process gas is transformed into plasma by the resultant electric field.
A coolant circulation line 102 extends through the electrode 132, on which the wafer 2 is mounted, or through the pedestal 134 to directly control the temperature of the wafer 2. The coolant is circulated through the line 102 with constant fluid pressure and fluid quantity while being cooled (or heated) by a chiller 100. The coolant may be an inert solution consisting of deionized water, an immobile solution diluted at a constant rate, or a Fluorinert solution such as a colorless and odorless Fluoro Carbon solution.
The chiller 100 provides a typical cooling cycle. The chiller 100 comprises a compressor to transform gas coolant at a low temperature and low pressure to gas coolant having a high temperature and high pressure, a condenser to transform the gas coolant having a high temperature and high pressure to fluid coolant at room temperature and having a high pressure, an expander to transform the fluid coolant at room temperature and high pressure to fluid coolant having a low temperature and low pressure, and an evaporator to absorb heat from the outside while transforming the fluid coolant at low temperature and low pressure to gas. With the operation of the compressor, the coolant is successively compressed and evaporated so that the coolant, in turn, radiates and absorbs heat. The cooled (or heated) coolant circulating through the coolant circulation line 102 passes through the inside of the electrode 132 so that a heat exchange is effected.
As described above, a temperature controlling apparatus (chiller) is disposed outside the semiconductor device fabrication facility F in which the wafer 2 is processed. The chiller 100 thus occupies a large amount of otherwise free space, and contributes to the expense necessary for maintaining the clean room in which the semiconductor fabrication facility is provided. Moreover, although the conventional chiller 100 is installed adjacent to the semiconductor device fabrication facility F to minimize the temperature losses, such temperature losses are inevitable because the coolant is circulated to and from the facility via the coolant circulation line 102. These temperature losses become especially significant when large-diametered wafers are processed because the chiller 100 must have a large cooling capacity in this case. Moreover, such a large chiller 100 requires so much space inside a clean room that a significant part of the cost associated with building the clean room can be attributed to the space necessary for accommodating the chiller.
In addition, any problem with the operation of the chiller 100 destabilizes the temperature of the wafer 2, thereby causing failures in the processing of the wafer 2. Also, the leakage of coolant adversely affects the chips on the wafer, thereby decreasing production yield and contaminating the clean room environment.
In addition, because the chiller 100 comprises a compressor, a condenser, an expander, and an evaporator, etc., the chiller requires a large amount of maintenance and hence, the expense associated therewith. Furthermore the chiller produces a serious amount of noise, and thus is deleterious to the work environment.
A first object of the present invention is to provide a heat exchanger which effects an efficient and precise amount of heat exchange with a thermal load, so as to be useful in a temperature control apparatus.
To achieve this object the present invention provides a thermoelectric element comprising a P-type semiconductor and an N-type semiconductor spaced apart from one another, a first electrical conductor comprising a negative electrode attached to one end of the P-type semiconductor and a positive electrode attached to one end of the N-type semiconductor, a second electrical conductor attached to the other ends of the semiconductors, and lower and upper electrically insulating thermoconductors attached to outer sides of the first and second conductors, respectively, thereby electrically insulating the conductive elements.
The thermoelectric element may comprise several pairs of the P-type and N-type semiconductors. In this case, the pairs are electrically connected to one another in series and/or parallel.
Another object of the present invention is to provide a thermoelectric-cooling temperature control apparatus for a semiconductor device fabrication facility which obviates one or more of the problems, limitations and disadvantages of the prior art.
In this respect, one specific object of the present invention is to provide a heat exchanger for a semiconductor device fabrication facility, which is disposed in the semiconductor device fabrication facility itself so as to not occupy space in the clean room.
Another specific object of the present invention is to provide a temperature control apparatus for a semiconductor device fabrication facility, which reliably maintains the temperature of a wafer stable during a fabrication process, and thereby enhances the yield of semiconductor devices.
Still another object of the present invention is to provide a temperature control apparatus for a semiconductor device fabrication facility, which has a simple structure, is compact and light-weight, and can be operated continuously for a long period of time without being maintained.
A still further object of the present invention is to provide a temperature control apparatus for a semiconductor device fabrication facility which is unlikely to contaminate the facility or the clean room in which the facility is disposed.
Still another object of the present invention is to provide a temperature control apparatus for a semiconductor device fabrication facility, which is inexpensive to maintain.
Another object of the present invention is to provide a temperature control apparatus for a semiconductor device fabrication facility, which produces little noise and thereby helps maintain a safe work environment.
Still another object of the present invention is to provide a thermoelectric-cooling temperature control apparatus for a semiconductor device fabrication facility which has a heat exchanger that can effect a large amount of heat transfer, and yet is easy to assemble to the facility, disassemble from the facility, to fix and to replace.
To achieve these objects, the present invention provides a temperature control apparatus having a heat exchanger disposed in a heat exchange relationship with the wafer support of the semiconductor device fabrication facility, the heat exchanger comprising a thermoelectric cooling element producing a Peltier Effect which causes the thermoelectric element to absorb and radiate heat according to the amount of current flowing through parts of the conductors in contact with each other.
A controller, such as a microprocessor, controls the amount of current supplied by a power source to the conductors of the thermoelectric cooling element, whereby the amount of heat exchange is controlled.
The heat exchanger can include heat radiation means to effect a final heat exchange outside of the processing chamber of the semiconductor device fabrication facility.